Thermally and electrically enhanced ball grid array packaging

ABSTRACT

Electrically and thermally enhanced die-up ball grid array (BGA) packages are described. A BGA package includes a stiffener, substrate, a silicon die, and solder balls. The die is mounted to the top of the stiffener. The stiffener is mounted to the top of the substrate. A plurality of solder balls are attached to the bottom surface of the substrate. A top surface of the stiffener may be patterned. A second stiffener may be attached to the first stiffener. The substrate may include one, two, four, or other number of metal layers. Conductive vias through a dielectric layer of the substrate may couple the stiffener to solder balls. An opening may be formed through the substrate, exposing a portion of the stiffener. The stiffener may have a down-set portion. A heat slug may be attached to the exposed portion of the stiffener. A locking mechanism may be used to enhance attachment of the heat slug to the stiffener. The heat slug may be directly attached to the die through an opening in the stiffener.

This application claims the benefit of U.S. Provisional Application No. 60/250,950, filed Dec. 1, 2000.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to the field of integrated circuit (IC) device packaging technology, and more particularly to substrate stiffening and heat spreading techniques in ball grid array (BGA) packages.

2. Background Art

Integrated circuit (IC) dies are typically mounted in or on a package that is attached to a printed circuit board (PCB). One such type of IC die package is a ball grid array (BGA) package. BGA packages provide for smaller footprints than many other package solutions available today. A BGA package has an array of solder balls located on a bottom external surface of a package substrate. The solder balls are reflowed to attach the package to the PCB. The IC die is mounted to a top surface of the package substrate. Wire bonds typically couple signals in the IC die to the substrate. The substrate has internal routing which electrically couples the IC die signals to the solder balls on the bottom substrate surface.

It would be advantageous to provide a thermally and electrically enhanced ball grid array (BGA) package that is smaller, cheaper, customizable and capable of superior performance when compared with conventional BGA packages. More specifically, it would be advantageous to provide an advanced BGA package that achieves: 1) enhanced thermal and electrical performance; 2) reduced package size; 3) increased flexibility of die configuration; 4) reduced ball pitch; 5) increased flexibility in circuit routing density; and 6) configurations with greater thermal spreading capabilities.

BRIEF SUMMARY OF THE INVENTION

Electrically and thermally enhanced die-up ball grid array (BGA) packages are described. In an embodiment, a BGA package includes a stiffener, substrate, a silicon die, and solder balls. The die is mounted to the top of the stiffener. The stiffener is mounted to the top of the substrate. A plurality of solder balls are attached to the bottom surface of the substrate. A top surface of the stiffener may be patterned. A second stiffener may be attached to the first stiffener. The substrate may include one, two, four, or other number of metal layers. Conductive vias through a dielectric layer of the substrate may couple the stiffener to solder balls. An opening may be formed through the substrate, exposing a portion of the stiffener. The stiffener may have a down-set portion. A heat slug may be attached to the exposed portion of the stiffener. A locking mechanism may be used to enhance attachment of the heat slug to the stiffener. The heat slug may be directly attached to the die through an opening in the stiffener.

Further embodiments, features, and advantages of the present inventions, as well as the structure and operation of the various embodiments of the present invention, are described in detail below with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE FIGURES

The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the invention.

FIG. 1 is a cross-sectional representation of a BGA package design in accordance with one embodiment of the disclosed method and apparatus.

FIG. 2 is a cross-sectional representation of another BGA package design in accordance with one embodiment of the disclosed method and apparatus.

FIG. 3 is a cross-sectional representation of another BGA package design in accordance with one embodiment of the disclosed method and apparatus.

FIG. 4 is a cross-sectional representation of another BGA package design in accordance with one embodiment of the disclosed method and apparatus.

FIG. 5 is a cross-sectional representation of another BGA package design in accordance with one embodiment of the disclosed method and apparatus.

FIG. 6 is a cross-sectional representation of another BGA package design in accordance with one embodiment of the disclosed method and apparatus.

FIG. 7 is a cross-sectional representation of another BGA package design in accordance with one embodiment of the disclosed method and apparatus.

FIG. 8 is a cross-sectional representation of another BGA package design in accordance with one embodiment of the disclosed method and apparatus.

FIG. 9 is a cross-sectional representation of another BGA package design in accordance with one embodiment of the disclosed method and apparatus.

FIG. 10 is a cross-sectional representation of another BGA package design in accordance with one embodiment of the disclosed method and apparatus.

FIG. 11 is a cross-sectional representation of another BGA package design in accordance with one embodiment of the disclosed method and apparatus.

FIG. 12 is a cross-sectional representation of another BGA package design in accordance with one embodiment of the disclosed method and apparatus.

FIG. 13 is a cross-sectional representation of another BGA package design in accordance with one embodiment of the disclosed method and apparatus.

FIG. 14 is a cross-sectional representation of another BGA package design in accordance with one embodiment of the disclosed method and apparatus.

FIG. 15 is a cross-sectional representation of another BGA package design in accordance with one embodiment of the disclosed method and apparatus.

FIG. 16 is a cross-sectional representation of another BGA package design in accordance with one embodiment of the disclosed method and apparatus.

FIG. 17 is a cross-sectional representation of another BGA package design in accordance with one embodiment of the disclosed method and apparatus.

FIG. 18 is a cross-sectional representation of another BGA package design in accordance with one embodiment of the disclosed method and apparatus.

The present invention will now be described with reference to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements. Additionally, the left-most digit(s) of a reference number identifies the drawing in which the reference number first appears.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a thermally and electrically enhanced ball grid array (BGA) packaging that is smaller, cheaper, customizable and capable of superior performance when compared with conventional BGA packages. More specifically, the present invention offers advanced BGA packages that achieve: 1) enhanced thermal and electrical performance; 2) reduced package size; 3) increased flexibility of die configuration; 4) reduced ball pitch; 5) increased flexibility in circuit routing density; and 6) optional configurations with or without the attachment of a heat sink.

Embodiments of the present invention may be used in a variety of electronic devices, including telecommunication devices, mobile phones, camcorders, digital cameras, network systems, printers, and testers.

Advantages of the various embodiments of the invention include: 1) an embedded heat spreader in the package for the silicon die to adhere onto, and a connection between the die and the heat spreader to provide thermal and electrical performance enhancement; 2) an option of a fully populated ball grid array assignment for circuit routing; 3) an option of multi-layer heat spreader structure to provide split and isolated ground; 4) an option of utilizing single, double or multi-layer metal circuitry substrate with or without plating traces and with or without conductive via connections to accommodate different thermal, electrical and design requirements; 5) exposed die attach pad for enhanced thermal performance; 6) drop-in heat slug for direct thermal and electrical conduction; 7) flexible range of ball pitch from 0.3 mm to 1.5 mm; 8) active ground connection capability from silicon die to motherboard through conductive slug attachment or through solder ball connects to the heat spreader; 9) high thermal conductive path; 10) low package profile compared with plastic ball grid array (PBGA) and other conventional BGA packages; and 11) wafer saw or punch format for maximized material utilization.

Embodiments of the present invention are described in detail below, and are designated as Designs 1 through 18.

Design 1—Fully Populated Package with Solid Grounding

FIG. 1 shows a BGA package 100, according to an embodiment of the present invention. BGA package 100 incorporates a substrate 130 with a single metal layer, and a heat spreader/stiffener 112 with selective plating. BGA package 100 includes substrate 130, stiffener 112, an integrated circuit die 114, a mold/glob top 120, a plurality of solder balls 122, a first wire connection 124, and a second wire connection 126.

Substrate 130 includes a base material/dielectric layer 102, a conductive metal layer 106, and a circuit mask 108. Metal layer 106 is attached to the bottom surface of dielectric layer 102 by an adhesive 104. Metal layer 106 is a conductive layer that is patterned with traces. Circuit mask 108 is applied to the top surface of dielectric layer 102. Dielectric layer 102 may be any one of PCB, FR4, polyimide, and ceramic dielectric materials.

Stiffener 112 is attached to the top surface of substrate 130 by an adhesive 110. Die 114 is attached to the top surface of stiffener 112 by a die attach epoxy 116. First wire connection 124 is coupled from a pin on die 114 to stiffener 112. A bondable plating surface 118 is formed on the top surface of stiffener 112 to enhance attachment of first wire connection 124 to stiffener 112. Second wire connection 126 is coupled from a pin on die 114 to a trace of metal layer 106. Mold/glob top 120 is formed over the top surface of stiffener 112 to encapsulate die 114 and first and second wire connections 124 and 126.

Preferably, copper is used to make metal layer 106, although other metals may also be used. Similarly, stiffener 112 is preferably made from copper so that it may provide a substantially rigid and planar surface, enhance the coplanarity of the different layers of substrate 130, and, at the same time, act as a heat spreader to help dissipate heat. Alternatively, other materials, such as aluminum or ceramic, may also be used to make the stiffener.

Preferably, bondable surface 118 is selectively plated, chemically deposited or electro-deposited on stiffener 112 for solid or float grounding purposes. Otherwise, stiffener 112 may be fully plated. Dielectric layer 102, preferably a polyimide tape, is patterned with openings or vias for accepting solder balls 122 so that solder balls 122 make electrical contact with the patterned conductive metal layer 106. The distance between centers of adjacent solder balls 122 is shown as ball pitch 128 in FIG. 1.

Table 1 shows example dimensions and ranges for some of the elements shown in FIG. 1:

TABLE 1 Element Thickness (mm) Base material/dielectric layer 102 0.025-2 Adhesive 104 0.012-0.25 Trace/Metal layer 106 0.012-0.35 Circuit mask 108 0.017-0.20 Adhesive 110 0.012-0.25 Stiffener 112 0.1-1 Thickness of die 114 0.15-0.8 Die attach Epoxy 116 0.025-0.075 Bondable plating surface 118 0.0005-0.05 Mold/Glob top 120 0.3-3 Solder ball 122 0.15-0.9 (collapsed height) Ball pitch 128 0.3-1.5 Design 2—Fully Populated Package with Solid Grounding

FIG. 2 shows a BGA package 200, according to an embodiment of the present invention. As shown in FIG. 2, BGA package 200 is basically the same as BGA package 100, except that it does not have an adhesive layer 104 between patterned dielectric layer 102 and patterned conductive metal layer 106. Furthermore, a first and second dimple design 202 and 204 are shown on stiffener 112 in FIG. 2. First and/or second dimple designs 202 and 204 on stiffener 112 (e.g., a protrusion or indention) are preferably introduced to enhance the adhesiveness of the molding compound or encapsulant material (i.e., mold/glob top 120) to the surface of stiffener 112 by increasing the total contact surface area. First and second dimple designs 202 and 204 may have any applicable dimensions.

Design 3—Fully Populated Package with Two Stiffeners and Symmetrical Segment Grounding

FIG. 3 shows a BGA package 300, according to an embodiment of the present invention. As shown in FIG. 3, BGA package 300 incorporates first stiffener 112 and a second stiffener 302, each with selective plating, to achieve split grounding. In BGA package 300, die 114 is mounted to the top surface of second stiffener 302. A third wire connection 306 is coupled from a pin on die 114 to bondable plating surface 118 on second stiffener 302. In an example embodiment, bondable plating surface 118 on the top stiffener, second stiffener 302, may be used for digital grounding, and bondable plating surface 118 on the bottom stiffener, first stiffener 112, may be used for analog grounding. A dielectric adhesive layer 304 is incorporated between first and second stiffeners 112 and 302 to ensure separated grounding.

Other features of BGA package 300 are similar to the corresponding features in BGA package 200.

Design 4—Fully Populated Package with Two Stiffeners and Asymmetrical Segment Grounding

FIG. 4 shows a BGA package 400, according to an embodiment of the present invention. As shown in FIG. 4, BGA package 400 is similar to BGA package 300 shown in FIG. 3, except that split solid grounding is done asymmetrically. In other words, bondable plating surfaces 118 are placed on the respective first and second stiffeners 112 and 302 asymmetrically.

Other features of BGA package 400 are similar to the corresponding features in aforementioned designs.

Design 5—Fully Populated Package with Enhanced Routability

FIG. 5 shows a BGA package 500, according to an embodiment of the present invention. As shown in FIG. 5, a substrate 502 of BGA package 500 incorporates two conductive layers, first metal layer 106 and second metal layer 504, that include traces. First circuit mask 108 is formed over the top surface of substrate 502, and a second circuit mask 506 is formed over the bottom surface of substrate 502. First and second metal layer 106 and 504 are separated by dielectric layer 102, which is preferably a polyimide tape. Dielectric layer 102 includes selective conductive vias 508 between first and second metal layers 106 and 504. By selectively connecting the metal layers through conductive vias 508, enhanced routing flexibility as well as enhanced electrical and thermal performance is provided.

Other features of BGA package 500 are similar to the corresponding features in aforementioned designs.

Design 6—Fully Populated Package with Enhanced Routability

FIG. 6 shows a BGA package 600, according to an embodiment of the present invention. As shown in FIG. 6, BGA package 600 is similar to BGA package 500 shown in FIG. 5 except that BGA package 600 includes a substrate 616 that has four conductive trace layers: a first metal layer 602, a second metal layer 604, a third metal layer 606, and a fourth metal layer 608. The metal layers are separated by dielectric layers with conductive vias. A first dielectric layer 610 separates first metal layer 602 and second metal layer 604. A second dielectric layer 612 separates second metal layer 605 and third metal layer 606. A third dielectric layer 614 separates third metal layer 606 and fourth metal layer 608. For example, second dielectric layer 612 may be a prepeg organic material. Solder balls 122 are attached to portions of fourth metal layer 608 exposed through second circuit mask 506.

As such, BGA package 600 provides superior routing flexibility to BGA package 500, and offers excellent electrical and thermal performance. Note that more conductive layers may be used. In that case, however, both the manufacturing cost and the package size (thickness) would increase accordingly.

Other features of BGA package 600 are similar to the corresponding features in aforementioned designs.

Design 7—Fully Populated Package with Enhanced Signal Integrity

FIG. 7 shows a BGA package 700, according to an embodiment of the present invention. As shown in FIG. 7, BGA package 700 uses conductive paths 702 to connect and ground selected solder balls 122 to stiffener 112. As such, BGA package 700 provides enhanced noise reduction, thus improved signal integrity, by grounding the discharge current through the ground bond (i.e., wire connection 124), stiffener 112, conductive paths 702, and solder balls 122, and discharge to a connecting motherboard (not shown).

Other features of BGA package 700 are similar to the corresponding features in aforementioned designs.

Design 8—Fully Populated Package with Enhanced Signal Integrity and Routability

FIG. 8 shows a BGA package 800, according to an embodiment of the present invention. As shown in FIG. 8, BGA package 800 is basically a combination of BGA package 500 shown in FIG. 5 and BGA package 700 shown in FIG. 7, providing enhanced routing flexibility and signal integrity. In other words, BGA package 800 is BGA package 700 with two conductive layers, first and second metal layers 106 and 504, instead of a single metal layer.

Other features of BGA package 800 are similar to the corresponding features in aforementioned designs.

Design 9—Partially Depopulated Package with Partially Exposed Stiffener

FIG. 9 shows a BGA package 900, according to an embodiment of the present invention. As shown in FIG. 9, substrate 130 of BGA package 900 has a “punched” opening or window that exposes a part of stiffener 112, shown as exposed stiffener portion 902. BGA package 900 improves thermal performance because heat may be readily dissipated via exposed stiffener portion 902 of stiffener 112. In addition, plating trace routability is also enhanced through the debussing window punched opening. It should be readily apparent to those of ordinary skill in the art that the size of the opening may vary depending on, for example, the desired size of an optional heat slug to be attached to stiffener 112 via the opening (as described in embodiments in the sections below related to Designs 11-14).

Other features of BGA package 900 are similar to the corresponding features in aforementioned designs.

Design 10—Partially Depopulated Package with Partially Exposed Stiffener

FIG. 10 shows a BGA package 1000, according to an embodiment of the present invention. As shown in FIG. 10, BGA package 1000 is similar to BGA package 900 shown in FIG. 9, except that BGA package includes substrate 502, which has two patterned conductive layers (first and second metal layers 106 and 504), instead of one metal layer, for enhanced routing flexibility. Substrate 502 has a punched opening or window, similar to that shown in substrate 130 in FIG. 9.

Other features of BGA package 1000 are similar to the corresponding features in aforementioned designs.

Design 11—Partially Depopulated Package with Drop-In Heat Slug

FIG. 11 shows a BGA package 1100, according to an embodiment of the present invention. As shown in FIG. 11, BGA package 1100 is similar to BGA package 900 shown in FIG. 9, but with an additional drop-in heat slug 1102 attached to the bottom surface of stiffener 112 by adhesive 1104. Adhesive 1104 is a conductive adhesive, epoxy, or solder. Heat slug 1102 allows direct conductive heat dissipation from die 114 through die attach epoxy 116, stiffener 112, adhesive 1104, and heat slug 1102 to an attached motherboard (not shown).

Other features of BGA package 1100 are similar to the corresponding features in aforementioned designs.

Design 12—Partially Depopulated Package with Drop-In Heat Slug

FIG. 12 shows a BGA package 1200, according to an embodiment of the present invention. As shown in FIG. 12, BGA package 1200 is similar to BGA package 1000 shown in FIG. 10, but with the addition of drop-in heat slug 1102. Heat slug 1102 allows direct conductive heat dissipation from the die 114 through die attach epoxy 116, stiffener 112, adhesive 1104, and heat slug 1102 to an attached motherboard (not shown).

Other features of BGA package 1200 are similar to the corresponding features in aforementioned designs.

Design 13—Partially Depopulated Package with Drop-In Heat Slug

FIG. 13 shows a BGA package 1300, according to an embodiment of the present invention. As shown in FIG. 13, BGA package 1300 is similar to BGA package 1100 shown in FIG. 11. The difference is that BGA package 1300 has an added locking mechanism for attaching drop-in heat slug 1102 to stiffener 112. The locking mechanism includes a bump 1302 on heat slug 1102 that fits into a slot 1304 in stiffener 112. The locking mechanism allows easy attachment and alignment of heat slug 1102 to stiffener 112. An adhesive 1306 is used to adhere bump 1302 in slot 1304. Adhesive 1306 may be a conductive adhesive, epoxy, or solder.

Other features of BGA package 1300 are similar to the corresponding features in aforementioned designs.

Design 14—Partially Depopulated Package with Drop-In Heat Slug

FIG. 14 shows a BGA package 1400, according to an embodiment of the present invention. As shown in FIG. 14, BGA package 1400 is similar to BGA package 1300 shown in FIG. 13, except it includes a substrate 502 that has two conductive layers (first and second metal layers 106 and 504) instead of a single conductive layer.

Other features of BGA package 1400 are similar to the corresponding features in aforementioned designs.

Design 15—Partially Depopulated Package with Partially Exposed Down-Set Stiffener

FIG. 15 shows a BGA package 1500, according to an embodiment of the present invention. As shown in FIG. 15, BGA package 1500 has a stiffener 112 with a lowered and exposed stiffener portion 1502. This “down-set” stiffener portion 1502 provides for a thinner package design. For example, as shown in FIG. 15, die 114 can sit lower in BGA package 1500 than in other BGA packages. The exposed stiffener 112 also enhances thermal performance similar to BGA package 900 shown in FIG. 9.

Other features of BGA package 1500 are similar to the corresponding features in aforementioned designs.

Design 16—Partially Depopulated Package with Partially Exposed Down-Set Stiffener

FIG. 16 shows a BGA package 1600, according to an embodiment of the present invention. As shown in FIG. 16, BGA package 1600 is similar to BGA package 1500 shown in FIG. 15, except that substrate 502 in BGA package 1500 includes two conductive layers (first and second metal layers 106 and 504) instead of a single conductive layer.

Other features of BGA package 1600 are similar to the corresponding features in aforementioned designs.

Design 17—Partially Depopulated Package with a One-Piece Stiffener/Die Paddle/Heat Slug

FIG. 17 shows a BGA package 1700, according to an embodiment of the present invention. As shown in FIG. 17, BGA package 1700 incorporates a one-piece stiffener/die paddle/heat slug 1702 such that die 114 sits directly on top of stiffener/die paddle/heat slug 1702. BGA package 1700 provides excellent thermal performance, as heat directly dissipates from die 114 through die attach epoxy 116 and stiffener/die paddle/heat slug 1702 to an attached motherboard (not shown).

Other features of BGA package 1700 are similar to the corresponding features in aforementioned designs.

Design 18—Partially Depopulated Package with a One-Piece Stiffener/Die Paddle/Heat Slug

FIG. 18 shows a BGA package 1800, according to an embodiment of the present invention. As shown in FIG. 18, BGA package 1800 is similar to BGA package 1700 shown in FIG. 17, except that substrate 502 of BGA package 1800 includes two conductive layers (first and second metal layers 106 and 504) instead of a single conductive layer.

Other features of BGA package 1800 are similar to the corresponding features in aforementioned designs.

Note that all of the above designs may be manufactured in wafer saw format for maximized material utilization.

Refer to Table 2 below, which provides a brief overview of the above described embodiments/designs.

TABLE 2 Design Description Advantages 1 1 ML substrate + thick Fully populated thermally stiffener with selective plating enhanced package (Use Adhesive Base Polymide) Ground bond on heat spreader 2 1 ML substrate + thick Fully populated thermally stiffener with selective plating enhanced package (Use Adhesiveless Base Polyimide) 3, 4 Two pieces stiffener with To achieve split ground selective plating function (analog & digital ground) with dielectric adhesive material 5 2 ML substrate + thick To improve routability, stiffener with selective plating electrical and thermal performance 6 4 ML substrate + thick Excellent routability, stiffener with selective plating electrical and thermal performance 7 1 ML substrate + thick To improve signal integrity stiffener with selective plating + for noise reduction by active ground ball connect to grounding the discharge heat spreader current through the ground bond, stiffener and discharge to the mother board 8 2 ML substrate + thick To improve routability, stiffener with selective plating + electrical and thermal active ground ball connect to performance heat spreader To improve signal integrity for noise reduction by grounding the discharge current through the ground bond, stiffener and discharge to the mother board 9 1 ML substrate + thick To improve the thermal stiffener with selective plating + performance by exposing the window opening die paddle through window punched opening To improve plating traces routability through debussing window punched opening 10 2 ML substrate + thick To improve routability, stiffener with selective plating + electrical and thermal window opening performance To improve the thermal performance by exposing the die paddle through window punched opening To improve plating traces routability through debussing window punched opening 11 1 ML substrate + thick Excellent thermal stiffener with selective plating + performance. Direct window opening + drop-in conductive heat dissipation heat slug from silicon thru epoxy, stiffener, heat slug to mother board To improve plating traces routability through debussing window punched opening 12 2 ML substrate + thick Excellent thermal stiffener with selective plating + performance. Direct window opening + drop-in conductive heat dissipation heat slug from silicon thru epoxy, stiffener, heat slug to mother board To improve plating traces routability through debussing window punched opening To improve rourability, electrical and thermal peformance 13 1 ML substrate + thick Excellent thermal stiffener with selective plating + performance. Direct window opening + drop-in conductive heat dissipation heat slug with mechanical from silicon thru epoxy, locking mechanism stiffener, heat slug to mother board To improve plating traces routability through debussing window punched opening To improve heat slug adhesion by increasing the contact surface area 14 2 ML substrate + thick Excellent thermal stiffener with selective plating + performance. Direct window opening + drop-in conductive heat dissipation heat slug with mechanical from silicon thru epoxy, locking mechanism stiffener, heat slug to mother board To improve plating traces routability through debussing window punched opening To improve routability, electrical and thermal peformance To improve heat slug adhesion by increasing the contact surface area 15 1 ML substrate + thick To improve the thermal stiffener with selective plating + performance by exposing the down set paddle + window die paddle through window opening punched opening To improve plating traces routability through debussing window punched opening Lower package thickness profile by applying down-set die paddle construction 16 2 ML substrate + thick To improve the thermal stiffener with selective plating + performance by exposing the down set paddle + window die paddle through window opening punched opening To improve plating traces routability through debussing window punched opening Lower package thickness profile by applying down-set die paddle construction To improve routability, electrical and thermal performance 17 1 ML substrate + thick Excellent thermal stiffener with selective plating + performance. Direct stiffener window opening + conductive heat dissipation tape opening + die paddle heat from silicon thru epoxy, slug stiffener, heat slug to mother board To improve plating traces routability through debussing window punched opening One-piece stiffener, die paddle and heat slug concept 18 2 ML substrate + thick Excellent thermal stiffener with selective plating + performance. Direct stiffener window opening + conductive heat dissipation tape opening + die paddle heat from silicon thru epoxy, slug stiffener, heat slug to mother board To improve plating traces routability through debussing window punched opening One-piece stiffener, die paddle and heat slug concept To improve routability, electrical and thermal performance Conclusion

Although the invention herein has been described with reference to particular embodiments, it is to be understood that the embodiments are merely illustrative of the principles and application of the present invention. It is therefore to be understood that various modifications may be made to the above mentioned embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention. For example, Design 5 could be modified to incorporate two stiffeners to achieve split grounding. In fact any of the above mentioned designs may be combined with any other design or designs to produce a new package. 

1. A ball grid array (BGA) package, comprising: a substrate that has opposing first and second surfaces, wherein said substrate has a window opening through said substrate that is open at said first surface and said second surface; a stiffener that has a first surface attached to said second surface of said substrate, wherein said stiffener further has a second surface having a mounting location for an integrated circuit (IC) die; and a heat slug that has a first surface attached to a portion of said first surface of said stiffener through said window opening, wherein said heat slug has a second surface that is capable of being mounted to a printed circuit board (PCB); wherein said portion of said first surface of said stiffener includes a first portion of a locking mechanism and said first surface of said heat slug includes a second portion of said locking mechanism, wherein said locking mechanism aligns said heat slug with said stiffener when coupled together.
 2. The package of claim 1, wherein said second portion of said locking mechanism includes a surface bump on said first surface of said heat slug; and wherein said first portion of said locking mechanism includes a slot in said portion of said first surface of said stiffener that corresponds to said surface bump; wherein said surface bump fits into said slot when said first surface of said heat slug is coupled to said portion of said first surface of said stiffener through said window opening.
 3. The package of claim 2, wherein said locking mechanism further includes an adhesive material to adhere said surface bump in said slot.
 4. The package of claim 1, wherein said first portion of said locking mechanism includes a surface bump on said portion of said first surface of said stiffener; and wherein said second portion of said locking mechanism includes a slot in said first surface of said heat slug that corresponds to said surface bump; wherein said surface bump fits into said slot when said first surface of said heat slug is coupled to said portion of said first surface of said stiffener through said window opening.
 5. The package of claim 4, wherein said locking mechanism further includes an adhesive material to adhere said surface bump in said slot.
 6. The package of claim 1, wherein said second surface of said heat slug attaches to the PCB when the package is mounted to the PCB.
 7. The package of claim 1, wherein said first portion of said locking mechanism is centrally located on said portion of said first surface of said stiffener.
 8. The package of claim 1, wherein said second portion of said locking mechanism is centrally located on said first surface of said beat slug.
 9. The package of claim 1, wherein said second portion of said locking mechanism consists of a surface bump on said first surface of said heat slug; wherein said first portion of said locking mechanism consists of a slot in said portion of said first surface of said stiffener that corresponds to said surface bump; and wherein said surface bump fits into said slot when said first surface of said heat slug is coupled to said portion of said first surface of said stiffener through said window opening.
 10. The package of claim 9, wherein said surface bump is centrally located on said first surface of said heat slug.
 11. The package of claim 9, wherein said slot is centrally located on said portion of said first surface of said stiffener.
 12. The package of claim 9, wherein said locking mechanism further includes an adhesive material to adhere said surface bump in said slot.
 13. The package of claim 1, wherein said first portion of said locking mechanism consists of a surface bump on said portion of said first surface of said stiffener; wherein said second portion of said locking mechanism consists of a slot in said first surface of said heat slug that corresponds to said surface bump; and wherein said surface bump fits into said slot when said first surface of said heat slug is coupled to said portion of said first surface of said stiffener through said window opening.
 14. The package of claim 13, wherein said surface bump is centrally located on said portion of said first surface of said stiffener.
 15. The package of claim 13, wherein said slot is centrally located on said first surface of said heat slug.
 16. The package of claim 13, wherein said locking mechanism further includes an adhesive material to adhere said surface bump in said slot.
 17. A method of assembling a ball grid array (BGA) package, comprising the steps of: (A) attaching a surface of a stiffener to a surface of a substrate that has a window opening therethrough to allow a portion of the surface of the stiffener to be accessed through the window opening; and (B) attaching a first surface of a heat slug to the accessible portion of the surface of the stiffener through the window opening, wherein the heat slug has a second surface that is capable of being mounted to a printed circuit board (PCB); wherein step (B) includes the step of (1) aligning the first surface of the heat slug with the accessible portion of the surface of the stiffener using a locking mechanism.
 18. The method of claim 17, wherein step (1) includes the step of: fitting a surface bump on the first surface of the heat slug into a slot on the accessible portion of the surface of the stiffener.
 19. The method of claim 18, wherein step (B) further includes the step of: (2) using an adhesive to adhere the surface bump in the slot.
 20. The method of claim 17, wherein step (1) includes the step of: fitting a surface bump on the accessible portion of the surface of the stiffener into a slot on the first surface of the heat slug.
 21. The method of claim 20, wherein step (B) further includes the step of: (2) using an adhesive to adhere the surface bump in the slot.
 22. The method of claim 17, wherein the locking mechanism is formed by the steps of: forming a bump on a surface of the heat slug; and forming a slot in the surface of the stiffener, wherein the bump is capable of fitting into the slot when the surface of the heat slug is attached to the surface of the stiffener.
 23. The method of claim 17, wherein the locking mechanism is formed by the steps of: forming a bump on a surface of the stiffener; and forming a slot in the surface of the heat slug, wherein the bump is capable of fitting into the slot when the surface of the heat slug is attached to the surface of the stiffener. 